Chimeric viral receptor polypeptides

Abstract

Target cell specificity of delivery vectors is provided by incorporation of a target cell specific binding domain by the use of any binding domain, which binds specifically to a binding site on the target cell. The binding site may be endogenous to the target cell, provided by engineering the target cell, or a suitable binding site may be associated with the target cell. Target cells may also be associated with a CVR polypeptide to provide specificity for the delivery vector. The association of the CVR polypeptide confers target cell specificity for a second virus host cell range, which specificity differs from the viral host cell range of the endogenous target cell or animal host cell viral receptors. The CVR polypeptide may thus comprise a chimeric virus binding site which binds a second virus env binding domain specific for a second virus host cell range, selected from at least one of the group consisting of amphotropic, polytropic, xenotropic, ecotropic and tissue specific.

What is claimed is: 
     
       1. A soluble viral receptor fusion protein for a murine ecotropic retrovirus comprising a) a target cell binding domain consisting of a single chain F(v) antibody fragment specific for a human cell, which target cell binding domain is covalently linked through a peptide linker to   b) an ecotropic retrovirus receptor domain consisting of a polypeptide having at least an 80% sequence identity with residues 238-244 of SEQ ID. NO: 8 or a corresponding domain of a murine ecotropic retrovirus receptor, which is residues 232-237 of SEQ ID. NO: 4.   
     
     
       2. The protein of claim 1 in which the target cell binding domain is specific for a human tumor cell. 
     
     
       3. The protein of claim 2 in which the target cell binding domain is B3(Fv). 
     
     
       4. The protein of claim 1 in which the receptor domain consists of a polypeptide having the sequence of residues 210-250 of SEQ ID. NO: 8 modified by the substitution  242  (Pro→Tyr). 
     
     
       5. The protein of claim 4 in which the receptor domain is further modified by the substitutions  239  (Glu→Asn),  240  (Gly→Val) and  244  (Val→Glu). 
     
     
       6. The protein of claim 1 which is B3(Fv)-Ex3mH13.